Circulating red blood cells (RBC) constitute the largest pool of biologically available nitric oxide (NO) in the mammalian organism. It has now been shown that NO-related bioactivity is released form human RBCs in an oxygen-dependent manner. The mechanism of NO export seems to involve a novel system whereby S-nitrosohemoglobin (SNO- Hb) transnitrosylates cysteine thiols in the cytoplasmic domain of the membrane RBC anion-exchanger 1 protein (AE1). The details of this novel RBC function stand to be elucidated. To characterize this system, the following specific aims have been formulated. 1) To identify the chemical nature of released NO species and to specific the target thiols in the cytoplasmic domain of AE1. 2) Determine the effects of S-nitrosylation AE1 function. 3) Characterize the NO exporter in sickle cell RBCs, a prototypical disease model fo hemoglobin dysfunction. 4) Develop a transgenic murine model with site-directed mutagenesis of AE1 cytoplasmic domain thiols transnitrosylated SNOHb. The abiding goals of this project are to gain a greater understanding of mechanisms in the RBC in both normal and disease states. The results of these studies underscore the potential but largely unexplored role of Hb- membrane interactions in the pathogenesis of the thrombotic diathesis, ischemic syndromes, oxidative disorders and hypertensive states that are associated with altered hematocrit, hemoglobinopathies (like sickle cell disease), and RBC membrane defects.